Streptococcus classification

Streptococcus classification
  • There are several species of Gram-positive, catalase-negative cocci in the genus Streptococcus.
  • They do not produce spores and are not mobile.
  • They are placed in pairs as well as chains of various lengths.
  • Some of these, such as Streptococcus pyogenes, are human diseases, whereas others comprise the typical flora of both humans and animals.

Different criteria are used to categorise streptococci:

1. Based on the need for oxygen

  • Aerobes and facultative anaerobes, like certain strains of Streptococcus
  • Obligate or strict anaerobes: Peptostreptococcus, for example.

2. Brown's classification, which is based on the presence of a hemolytic pattern on blood agar

  • facultative anaerobic and aerobic On the basis of their hemolytic ability or their blood agar pattern, streptococci are further categorised.
  • J.H. Brown described it in 1919.
There are three types of streptococci based on this.

- Alpha-hemolytic Streptococci:
  • show signs of partial hemolysis (1-2mm wide)
  • Add a greenish tinge surrounding the colony and a few persistent, unhemolyzed RBCs, for example. Streptococci with viremia and Streptococcus pneumoniae
- Beta-hemolytic Streptococci:
  • demonstrate a large area of total hemolysis (2-4 mm wide)
  • the majority of streptococcal infections, such as pyogenes streptococcal
- Non-hemolytic Streptococci:
  • Furthermore known as gamma-hemolytic streptococci
  • Do not in any way provoke hemolysis
  • typically not harmful, such as Streptococcus faecalis, which is currently classified in the new genus Enterococcus.

3. Lancifield classification or serological classification:

  • This concept, often referred to as serological grouping, was proposed by Rebecca Lancefield in 1933.
  • This system is used to categorise the majority of beta-hemolytic strains as well as certain alpha-hemolytic and non-hemolytic bacteria.
  • It is based on the variation of group-specific polysaccharide antigen on Streptococci cell wall.
  • There are 20 Lancifield groups of streptococci, ranging from A to V. (except I and J)
    • Group A: Streptococcus pyogenes
      • Group A streptococci i.e. pyogenes are further sub divided into approximately 80 serotypes by Griffith according to their specific surface proteins (M, T and R). M-protein is the most important one.
      • The pathogenicity of Streptococci depends on the presence of hyaluronic acid capsule and surface M-protein.
    • Group B: Streptococcus agalactiae
    • Group C: Streptoccus equi
    • Group D: Enterococcus
    • Others (group E to V)

4. On the basis of 16s rRNA sequence:

The comparative study of 16s rRNA sequences further divides the genus Streptococcus into six groupings.

  • Pyogenic group:
    • Consists of predominantly beta-hemolytic species that are pathogenic in humans or animal species.
    • e.g. Streptococcus pyogenes, S. agalactiae
  • Anginosus group:
    • Found in the human oral cavity, gastrointestinal tract and genital tracts as normal flora
    • Sometimes isolated from infections
    • e.g. Streptococcus anginosus, S. intermedius
  • Mitis group:
    • Includes several oral streptococci
    • e.g. Streptococcus mitis, S. pneumoniae
  • Salivarius group:
    • Consists of both dairy streptococci and species found in the human oral cavity
    • e.g. Streptococcus salivarious, S. thermophiles
  • Bovis group:
    • Inhabits the intestinal tract of several animals species and sometimes humans
    • e.g. Streptococcus bovis, S. equines
  • Mutans group:
    • Mainly colonize tooth surfaces of humans and a number of animal species.
    • e.g. Streptococcus mutans, S. ferus

5. Shermann’s Divisions (On the basis of physiological characteristics):

  • Sherman made the suggestion in 1937.
  • He classified streptococci into the following four groups based on hemolytic response, group carbohydrate antigens, and phenotypic testing (mainly fermentation and tolerance tests):
    • Pyogenic division:
      • beta-hemolytic strains that are present and have specific group antigens (A, B, C, E, F, and G)
      • This split of the streptococci is comparable to the serological classification-based identification methods used today.
      • e.g. pyogenes streptococcal
    • Viridans division:
      • included strains of streptococcal bacteria that weren't beta-hemolytic or tolerant of high pH growing conditions.
      • They did not thrive at 10°C and could not tolerate salt.
      • The majority of them are typical human upper respiratory tract flora.
    • Lactic division:
      • strains utilised in the production of dairy products are included.
      • not connected to infections in people
      • mid-1980s, it was reclassified as the genus Lactococcus.
      • These groupings don't hemolyze.
      • e.g. Lactococcus
    • Enterococci division:
      • may flourish in broths with a high pH and can stand up to a lot of salt.
      • has a broad temperature range for growth (10 to 45 °C)
      • They are the typical intestinal flora of humans, such as Enterococcus

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